1. Field of the Invention
The present invention relates to integrated circuit structures incorporating monocrystalline semi-conductor zones dielectrically isolated from the substrate which supports them.
2. Description of the Prior Art
These structures are differentiated from the conventional structures in which the integrated circuit elements are formed directly in the volume of semi conductor substrate and are only isolated from each other by reverse bias junctions. They are used when it is desired to have a more efficient isolation than junction isolation.
The processes used for forming a dielectric isolation are expensive and difficult to put into practice.
Among them may be mentioned the use of completely isolating substrates such as corindon instead of a semi conductor substrate; monocrystalline silicon is grown on the substrate and the silicon is etched so as to leave only separate islets which are dielectrically isolated from each other since they rest on the isolating substrate. This technique is delicate for corindon is a fragile material, heavy and difficult to work, and unable to stand up to thermal shocks. In addition, the crystalline quality of the silicon deposited on the corindon is not very good.
There may also be mentioned complex and expensive implementation techniques in which, by different deposits and reversal of silicon wafers, completely isolated silicon islets may be created (EPIC technique).
The recrystallization of amorphous silicon deposited on a silicon substrate coated with isolating oxide is also a technique for forming dielectrically isolated islets on the substrate, but the crystalline quality of these islets obtained by recrystallization of amorphous silicon is relatively poor (presence of grains at the edge of the recrystallized zone).